Here's my super exciting new daily.
For the spacer, I found that when I bolted my rear wheel to the hub while the car was jacked up, the inner edge of the wheel hit the spring of the coil. So I had to get the little spacer to clear the rubbing. When I let the car back down the spring is nowhere near the wheel because it is compressed..... but I wanted to make sure it bolted up nice and flush, so hence the 3mm spacer.
It wasn't 100% neccesary as I could have used two jacks to compress the spring while it was in the air, but I spent $6 on spacers instead of another $50 on another jack.